The recently established high prevalence of undiagnosed sleep apnea has raised concerns about the public health burden and health care costs associated with this condition. Sleep apnea is thought to lead to a constellation of chronic and acute health problems which may have significant impact on health care costs, functional status and perceived well-being. The repeated hypoxia of sleep apnea, with its accompanying arousals and spurts of sympathetic nerve activity, has been shown to contribute to daytime sleepiness, decreased cognitive function, impotence, injury from accidents and affective disorders. Sleep apnea is also believed to contribute to the development of major chronic conditions such as hypertension, stroke, coronary heart disease, myocardial infarction and congestive heart failure. The Wisconsin Sleep Cohort Study with its established community-based cohort, recently evaluated for sleep apnea in our sleep laboratory, puts us in a unique position to address the health status and health care costs associated with undiagnosed sleep apnea. The cohort, established via a community-based probability sample, contains 978 employed persons aged 30- 60. A two-stage sampling scheme ensured that 30% of the cohort has at least mild sleep apnea. Importantly, over 90% of the cohort members receive medical care through one of four health maintenance organizations in Madison. Procedure/service codes can therefore conveniently be obtained from the financial records of these HMOs, and will be collected for all covered medical services received by the cohort in two calendar years. Overall health status will be measured using the SF-36. Analyses will compare patterns of health care utilization and imputed costs among persons with sleep apnea to those of persons without the disorder. The odds ratios for utilization of various medical services will be calculated. Detailed analyses will consider how the degree of sleep apnea relates to utilization and cost. The components of the SF-36 will also be correlated with the degree of sleep apnea. Other analyses will investigate observed gender differences in referral for sleep apnea work- up. In the current environment with proliferation of expensive diagnostic laboratories and other technologies for diagnosis and treatment for sleep apnea, our community-based data will provide health policy makers and health care managers urgently needed information on the medical care utilization by persons with sleep apnea.